[11:06:06 ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'rewards' in plugin Rewards v1.4
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:168) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.craftbukkit.v1_19_R3.CraftServer.dispatchCommand(CraftServer.java:943) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleCommand(ServerGamePacketListenerImpl.java:2616) ~[?:?]
        at org.bukkit.craftbukkit.v1_19_R3.entity.CraftPlayer.chat(CraftPlayer.java:723) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.citizensnpcs.util.Util.runCommand(Util.java:393) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.trait.CommandTrait$NPCCommand.run(CommandTrait.java:538) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.trait.CommandTrait$1.lambda$runCommand$2(CommandTrait.java:308) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.trait.CommandTrait$1.runCommand(CommandTrait.java:312) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.trait.CommandTrait$1.run(CommandTrait.java:272) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.trait.CommandTrait.dispatch(CommandTrait.java:319) ~[Citizens-2.0.31-b3100.jar:?]
        at net.citizensnpcs.EventListen.onPlayerInteractEntity(EventListen.java:470) ~[Citizens-2.0.31-b3100.jar:?]
        at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor372.execute(Unknown Source) ~[?:?]
        at org.bukkit.plugin.EventExecutor$2.execute(EventExecutor.java:77) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:77) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:git-Purpur-1985]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:126) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:617) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl$6.performInteraction(ServerGamePacketListenerImpl.java:2902) ~[?:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl$6.a(ServerGamePacketListenerImpl.java:2952) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundInteractPacket$InteractionAction.dispatch(ServerboundInteractPacket.java:131) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundInteractPacket.dispatch(ServerboundInteractPacket.java:80) ~[?:?]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleInteract(ServerGamePacketListenerImpl.java:2891) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundInteractPacket.handle(ServerboundInteractPacket.java:67) ~[?:?]
        at net.minecraft.network.protocol.game.ServerboundInteractPacket.handle(ServerboundInteractPacket.java:12) ~[?:?]
        at net.minecraft.network.protocol.PacketUtils.lambda$ensureRunningOnSameThread$0(PacketUtils.java:51) ~[?:?]
        at net.minecraft.server.TickTask.run(TickTask.java:18) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:153) ~[?:?]
        at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[?:?]
        at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1369) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:197) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:126) ~[?:?]
        at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1346) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1339) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:136) ~[?:?]
        at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1317) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1205) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:325) ~[purpur-1.19.4.jar:git-Purpur-1985]
        at java.lang.Thread.run(Thread.java:833) ~[?:?]
Caused by: java.lang.IllegalArgumentException: Material cannot be null
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:145) ~[guava-31.1-jre.jar:?]
        at org.bukkit.inventory.ItemStack.<init>(ItemStack.java:98) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.inventory.ItemStack.<init>(ItemStack.java:86) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.inventory.ItemStack.<init>(ItemStack.java:73) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        at me.sneklingame.rewards.util.GUI.openGUI(GUI.java:89) ~[Rewards.1.4.jar:?]
        at me.sneklingame.rewards.commands.RewardCommand.onCommand(RewardCommand.java:38) ~[Rewards.1.4.jar:?]
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[purpur-api-1.19.4-R0.1-SNAPSHOT.jar:?]
        ... 39 more